Patent GB-576910-A (GB)
Title: Improvements in the bleaching of organic materials
IPC: D06L4/70
Filed: 1944-02-01
Abstract: Organic materials other than cellulose, including artificial fibres, e.g. cellulose acetate and nylon; sponges; walnut shells; synthetic resins, are bleached by subjection to the simultaneous action of a chlorite and an aldehyde in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g. sodium or calcium chlorite, being preferred. Effective aldehydes include aliphatic, heterocyclic, aromatic and other carbocyclic aldehydes, specified compounds being formaldehyde, acetaldehyde, paraformaldehyde, furfural, benzaldehyde and also five and six carbon atom aldose sugars and inverted sugars.  Temperature and concentration are variable over a wide range and the ratio of chlorite to aldehyde is materially reduced by employing as adjuvants, buffer salts, e.g. sodium or disodium orthophosphate.  Bleaching may be effected by admixing the material with the aldehyde in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature usually ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In examples: (1) cellulose acetate rayon fabric is improved in colour by immersion for 1 hour in an aqueous mixture at 60 DEG  C., comprising pH 7 phosphate buffer solution, aqueous sodium chlorite and dilute formalin; (2) sponge is bleached by immersion for 1 hour in an aqueous solution containing sodium chlorite and formaldehyde at 50 DEG  C. and pH 6.6.ALSO:Organic materials other than cellulose, including carbohydrates, e.g. starch, are bleached by subjection to the simultaneous action of a chlorite and an aldehyde in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g. sodium or calcium chlorite, being preferred. Effective aldehydes include aliphatic, heterocyclic, aromatic and other carbocyclic aldehydes, specified compounds being formaldehyde, acetaldehyde, paraformaldehyde, furfural, benzaldehyde and also five and six carbon atom aldose sugars and inverted sugars. Temperature and concentration are variable over a wide range and the ratio of chlorite to aldehyde is materially reduced by employing as adjuvants, buffer salts, e.g. sodium or disodium orthophosphate. Bleaching may be effected by admixing the material with the aldehyde in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature usually ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In an example, crude corn starch suspended in water, is bleached at 50 DEG  C. and initial pH 7 by treatment with a mixture of aqueous sodium chlorite and aqueous formalin.ALSO:Organic materials other than cellulose including carbohydrates, e.g., sugar are bleached by subjection to the simultaneous action of a chlorite and an aldehyde in aqueous solution maintained at pH not less than 7, alkali and alkaline earth chlorites, e.g., sodium or calcium chlorite, being preferred. Effective aldehydes include aliphatic, heterocyclic, aromatic and other carbocyclic aldehydes, specified compounds being formaldehyde, acetaldehyde, paraformaldehyde, furfural, bensealdehyde and also five and six carbonatom aldose sugars and inverted sugars.  Temperature and concentration are variable over a wide range and the ratio of chlorite to aldehyde is materially reduced by employing as adjuvants, buffer salts, e.g., sodium or disodium orthophosphate.  Bleaching may be effected by (a) admixing the materials, either molten or in an aqueous solution, with a chlorite in presence of water and adding the aldehyde thereafter or (b) admixing the material with the aldehyde in presence of water and subsequently adding the chlorite, maintaining the resultant mixture at a temperature usually ranging from room temperature to approximately 100 DEG  C. for an appropriate period and thereafter cooling and separating.  In an example crude brown sugar in aqueous solution is treated at 40 DEG  C. for 1 hour with an aqueous mixture buffered at pH7 and containing sodium chlorite solution and formalin.  A check test, omitting formalin fails to effect bleaching.